Piston



March 31, 1936.

v J. S. DCNALDSQN PISTON Original Filed Aug. 24, 19:52

2 Sheets-Sheet 1 T ial.

A; ATTORNEY Reissues! Mar. 31, 1936 UNITED STATES PATENT OFFICE PISTONOriginal No. 1,904,126, dated April 18, 1933, Serial- No. 630,215,August 24, 1932. Application for reissue April 16, 1935, Serial No.16,659

11 Claims. (01. 309-20) This invention relates to pistons, and moreparticularly to pistons for internal combustion engines.

In the construction and operation of internal combustion engines, one ofthe principal factors to be taken into consideration is the diiferentialexpansion and contraction of the cylinder and piston under the varyingtemperatures which they assume and which extend over a large range inthe normal or usual operation oi the engine. Generally the cylinder iswater-jacketed and aircooled. The piston, owing to itslocation andmovement, is neither water-cooled nor controlled as ,to temperature by aiorced circulation or air." According to prevailing practices, thecylinder blocks of internal combustion engines are oi cast iron, whereasthe pistons are of light aluminum alloy having a higher coeiiicient ofheat expansion than the metal 01' the cylinder blocks. By reason ofthese differences in the cooling or the cylinder and the piston, andalso because of the diflerent metals 01' which they are made, a seriousproblem of compensation for differential expansion and contraction ispresented. The

piston should have a reasonably close flt with the cylinder throughoutthe temperature range. The diiiiculty to be overcome is that a suitablefit between the piston and cylinder when the engine is cold has a strongtendency to become a binding fit when the engine is warm, whereas, uponthe other hand, if the fit is made suitable under warm engineconditions, the fit becomes too loose under cooler conditions.

To overcome this diiliculty, pistons have been made with split skirts.But where a skirt is slotted down one side, the wrist pin bearing of thepiston acts as a tie preventingrunitorm expansion and as a strut inopposition to contraction. This results in the piston taking a shape,when heated, which is non-coniormant with the shape of the cylinder andis usually followed by a permanent deformity of the piston in the shapeit assumes when hot.

It is one of the objects of the present invention to provide aneffective means of controlling the diil'erential expansion of a pistonand its cylinder whereby a suitable sliding fit is efiected andmaintained throughout all of the temperatures of a reasonable operatingrange;

Another object of the invention is to provide an improved connectionbetween a piston and its connecting rod'by which it becomes possible toremove and insert the piston through the top of the cylinder withoutdisconnecting the connecting rod from the crank shaft. According to thepresent invention, a piston may be quickly and easily removed when it isdesired, for example, to

renew the rings, and as quickly and easily re-' placed in position,without disturbing the operative condition of the connections below thepiston, as is generally required in prior' constructions.

Other objects of the invention are to provide for the equalization ofwear on the piston and to provide for-adjustments to compensate for wearat the bearing connection between the rod and i the piston.

'Other objects will be in part obvious and in part pointed outparticularly as the description of an embodiment of the inventionproceeds. To the accomplishment of these objects the invention involvesa piston divided at its wall into two parts,-a head or ring-supportingportion and a skirt portion, the two portions being so related that aminimum of heat will pass from. the head portion to the skirt portion.

The head portion, being exposed to the hot gases in the cylinder, israised to a relatively high temperature. This is not harmful, so far asexpansion is concerned, since the head portion (exclusive of its rings)does not have to fit the cylinder closely. The piston is guided and heldin alignment by the skirt portion and hence the latter must fit thecylinder reasonably closely at all engine temperatures. For this reasonit is necessary to minimize difierential expansion and contraction bykeeping the skirt portion sufliciently cool to maintain an effective andunbinding seal. This involves controlling the flow of heat from the headportion to the skirt portion by making the body which connects the headand skirt portions long and small in cross-section, and by soconstructing and locating the members of such body that they are as.much exposed as possible to the cooling action of the oil splashed upfrom the crank-case and of the circulating air in the latter.

One of the most satisfactory ways of connecting the head and skirtportions is through the medium oi a central body having a plurality ofdownwardly and outwardly extending spaced legs, the upper end of thecentral both? portion merging with the head and the lower ends of thelegs merging with the lower part of the skirt portion. The use of spacedlegs allows the oil and air to reach all sides of such connectingportions and thereby exert a maximum cooling eifect.

The merging of such legs with the lower part of the skirt portion,instead of the middle or upper part thereof, not only extends thedistance that coolest part of the cylinder walls. The cylinder wallsbecome heated by the hot gases and the parts exposed to such hot gasesthe longest time have the highest temperature. Hence, the temperature ofthe cylinder wall surface decreases from the top of thecylinderdownward. As the skirt contacts with the cylinder walls, heatpasses from the former to the latter, and the cooler any part of thecylinder wallsis with respect to the part of the piston skirt in contacttherewith the greater the amount of heat which will pass from such partof the skirt to the-cylinder walls. The skirt is hottest in the zonewhich receives heat by conduction from the top of the piston. In thepresent case, this zone of maximum temperature is adjacent the bottom ofthe skirt. As this zone of maximum skirt temperature contacts with thecoolest zone of the parts of the cylinder walls which contact with thepiston skirt, the heat transfer will be a maximum.

The usual wrist-pin type of connection results in unequal wear on thepiston and cylinder, the wear taking place principally along twodiametrically opposite longitudinal zones of the piston. By providing aball-and-socket connection between the piston and the connecting rod,and

providing means for turning the piston on each cycle through a variableangle, the piston is caused to wear equally around its periphery and thescoring of either the piston or cylinder wall is avoided.

One of the most satisfactory methods of turning the piston is to soshape the latter that it is turned by the natural forces developed inthe operation of the engine. This method not only obviates the need ofadditional moving mechanical parts, but also results in the turning ofthe piston through a variable angle, thereby avoiding the scoring orgrooving which might result if the piston and cylinder walls wereperiodically brought into the same relative angular position.

The ball-and-socket type of connection between the piston and itsconnecting rod is admirably adapted for pistons of the type in which theskirt is connected to the body by a plurality of downwardly andoutwardly extending spaced legs, for the reason that all parts of thepiston may be symmetrically arranged about the piston axis.

This type of connection is also readily adapted for making the piston sothat it can be detached from the connecting rod from the upper side ofthe piston and then withdrawn through the top of the cylinder. Thisfollows from the fact that the bearing surfaces in a ball-and-sockettype connection are localized adjacent the axis of the piston, so that arelatively small open-topped chamber in the center of the pistonsufficesto contain the ball-head of the connecting rod and the upper andlower bearing blocks or elements therefor.

An approved embodiment of the invention is shown, by way of example, inthe accompanying drawings, wherein:

Fig. 1 is a longitudinal, axial section through the piston and the upperpart of the connecting rod, on the line Il of Fig. 2;

Fig. 2 is a bottom plan view of the piston, the connecting rod beingshown in section;

Fig. 3 is a top plan view of the piston;

Fig. 4 is a section on the line 4-4 of Fig. 1; and

and the cylinder.

threaded recess in the end of the stud 2|. external and internal threadson the stud 2| Fig. 5 is a section of the upper part of the piston onthe line 5-5 of Fig. 3.

The piston comprises two main parts, a head portion generally designatedas l0, which carries the usual rings II, and a skirt portion l2, which,as shown, is peripherally continuous. The head portion is formed of anannular top part IS, a ring-supporting part or wall I extending. fromthe outer periphery thereof, and a central body portion I5 extendingfrom the inner periphery of such top part. Extending from the bodyportion l5 are a plurality of symmetrically arranged downwardly andoutwardly extending forked legs l6 merged at their lower ends withthelower half of the skirt portion. As the legs I6 form the onlyconnection between the body and skirt portions, any heat transferred byconduction from the top of the piston to the skirt has to flowthroughthe tubular body part l5 and the legs IS. The latter are exposedon all sides to the cooling action of the oil splashed up from thecrankcase and of the air in the latter and the .the skirt or provideother similar means forallowing for difierential expansion between theskirt Preferably the piston skirt is formed slightly conical, with thelarger end next to the piston head. The purpose of this will hereinafterappear.

The connection between the piston and its connecting rod I I is of theball-and-socket type to allow the piston to turn about the end of theconnecting rod. The connecting rod is provided with a ball-head 20,formed with a diametrical passage therethrough, threaded in its lowerpart for engagement with a threaded stud 2| on the upper end of theconnecting rod. The ball-head is locked in position by a screw 22extending through the upper part of such passage and having threadedengagement with an internally The are made right-hand and left-hand,respectively, so that any tendency of the ball to unscrew from the endof the stud 2| tends to tighten the grip of the locking screw 22.

The ball-head 20 is located within a chamber consisting of the bore ofthe tubular body part I5. At the lower end of this chamber is a bearingelement 25, to advantage formed separately from the body part l5 andsupported by an inwardly extending sho ulder 2|. The wall of the chamberabove the bearing element 25 is threaded for engagement with an upperbearing element 26. The piston, as will be shown later, is constructedso that it turns in a clockwise direction, so that, if the threads onthe upper bearing ele,- ment are left-hand, the rotation of the pistonwill tend to keep the upper bearing element tightly its home position.The bore of the tubular body part I5 is widened above Ithe threaded partwhich engages the upper bearing element and is formed with right-handthreads. A right-hand-threaded lock nut 30 is engaged with the threadedupper part of the chamber. Due to the friction between the upper bearingelement and the lock nut, these parts tend to turn as a unit, and, in sofar as they do so turn,

Looking at the top of the piston, the direction the turning movementtightens the engagement of one or the other of these parts with theirrespective threads on the chamber wall. As, however, vibration may tendto loosen the lock nut, a spring II is provided, connected at one end tothe upper bearing element and at the other to the lock nut and tensionedso that the spring tends to turn these two parts in opposite directions.The result of this construction is that, as one part has a right-handand the other a left-hand thread, each part tends to be moved by thespring in a direction either away from or toward the other, so as toloosen or tighten the lock nut. The parts must be so connected that theparts tend to tighten, i. e., they must be moved by the spring towardeach other so as to increase theiriction between the two parts.

The upper bearing element is formed with an upstanding hexagonal boss 82to enable such element to be engaged by a socket wrench. The lock nut ismade hollow and is formed with a hexagonal inner face so as to beengaged by a socket wrench. In the annular space between the outer faceof the boss 32 and the inner face of the lock nut is arranged the spring3|. One end of this spring is bent inwardly for insertion into a radial,hole 35 in the boss 32. The other end of this spring is bent outwardlyfor insertion into one or other of a series of radial holes 36 inthelock nut. In assembling the piston, the bearing element 26 is screweddown to its desired position, then the lock nut is screwed down until itengages the bearing element, next the inwardly extending end of thespring 3| is slipped into the hole 35, and finally the other end ispulled around anti-clockwise until it is brought opposite and allowed toslip into one of the holes splashed up from the crank-case. For this-pur36 under tension. The spring is then under tension, so that it tends toturn the lock nut in a clockwise direction and the upper bearing elementin an anti-clockwise direction, thereby firmly holding such parts inlocked relation. Advantageously, the boss 32 is groovedcircumferentially, as shown in Figs. 1 and 4, to hold it in position andto allow greater space for the spring 3|. 1 4

After the lock nut has been adjusted and the spring inserted, the top ofthe chamber is closed by a threaded cap 40. This cap is formed with tworecesses ll for engagement by a key. Since the piston is free to turnabout the connecting rod, means should be provided for holding thepiston so that it cannot turn while the upper bearing element, lock nutand cap are being screwed up orunscrewed. The: means shown comprisethreerecesses 42in the top part II oi'1the piston ada'ptedto be engaged'by'three' pins on a ring formedwith a laterally extending handle. 1 Theball-and-socket joint is lubricatedby pose a series of holes 5. aredrilled through the tubular part ii to permit oil to pass into thecentral chamber wlthinsaid part. The passage of oil therethrough isaided by making these holes inclined 'upwardiy, as shown. These holesare above the top of the boss 32, so that oil entering through suchholescollects aroundthis boss and finally runs over its top'and down anoil passage il axially formed therein.

The upper surface of the top "part "of the piston is formed with threerecesses tithe bottoms of which slope downwardly in directionstransverse with respect to the radii of the piston.

of downward slope is clockwise. Intermediate each of these slopingsurfaces are surfaces lying in radial planes.

It has been found that a piston constructed, and associated with aconnecting rod, as above described, rotates intermittently throughangles of a varying number of degrees. In the normal operation of theengine, it has been observed that this rotation is in a clockwisedirection as the piston is viewed from the top as in Fig. 3. By reasonof the use of this construction, exceptional uniformity of wear of thecylinder walls is obtained, and the scoring, or grooving, which resultsfrom constant travel of a piston held rotatively or allowed to turn onlyin predetermined angles, is prevented. Caliper tests of the cylinderwalls of an engine equipped with the present arrangement, made after theengine has driven a car a great many thousand miles, show a maintainedtruly cylindrical bore.

angles of varying degree is believed to be due to forces developed onthe power cycle of the engine acting upon the upper surface of thepiston. It is believed that the initial impact of the explosive waveagainst the vertical wall rising from the base of whichever one of therecesses l5 rests in appropriate position causes a movement of thepiston about its axis and that this movement is irregular owing tovariations in the explosive forces and varying angular positions of thevertical faces of the piston head when the forces are applied. Whateverthe correct theory may be in regard to this, the fact is that the pistonrotates, and that all of the pistons so constructed-and arranged in thecylinders of an engine rotate in the same direction in the normaloperation of the engine.

A piston constructed as above described may be inserted in or removedfrom its cylinder from the upper side of the latter. To remove the.piston, the cap 40 is unscrewed, spring 3| detached and lock nut 30 andupper bearing element 26 unscrewed. The locking screw 22 is alsoremoved.

- The piston is then pushed down in the cylinder from the end of theconnecting rod. The piston The pismay then vbe lifted out of thecylinder; ton may be reinserted by reversing the above operations.

The universal mounting of the piston on the connecting rod allows forthe wear-equalizing rotary movement ofthe piston, aswe1l as permittingthe relative angular movement of the.

piston and connecting rod. -Such a mounting may be most effectivelyemployed in'pist'on. asi semblies where the piston is provided with asubstantial skirt which avoids tilting of thehead and injury totheparts. In the presentcase the iston construction is particularlyadapted to type inasmuch as the separate skirt portion of thepiston hasan upper region that is substantial--:v

ly segregated ,or isolated from the combustion t e employment of auniversal mounting of ball:

The cause of the intermittent rotation of the piston through slightlytapered skirt may be machined nearly-- to the size of the cylinderboreand will act as a guide under all conditions and temperatures.

preventing the head of the piston from tilting or tipping in ;itstravelin the cylinder. When the engine temperatures are raised, as bycontinued operation, the slight amount of heat transferred tion of wearon the cylinder walls.

through the legs of the piston body to the lower region of the skirtexpands that portion of the skirt to substantially the same diameter asthe upper, cooler, portion, and supplements the guiding action of theupper portion. Thus a highly desirable operating condition isestablished. The piston is reciprocated by an operating connectiondirected at a single central point. The major portion of the pistonwall, that is, the skirt, has a restricted range of expansion andcontraction due to its isolation from the influence of the highertemperatures. Such temperatures as are efl'ective on the skirt assistthe guiding function thereof. The piston is allowed to rotate and thedriving force is applied centrally within. The guiding is doneexteriorly over a substantial area extending ahead of,,and to the rearof, the point 01' application of the driving force. Under thetemperature range of ordinary engine operation the piston does not bindor slap, the guiding is 0! a character which prevents tilting of thepiston and consequent scoring of the cylinder, and the variable rotativemovements of the piston keep the wear uniform on both the piston and thecylinder.

It is to be noted that the compression head of the piston may be varied-without altering the association of the connecting rod with the crankshaft, which is not possible in conventional present day construction.To vary the compression head, the cap, upper bearing block, the ballhead of the connecting rod and the lower bearing block are removed inthe manner previously herein described. If it is desired to decrease thecompres sion head, shims are inserted below the lower bearing block. Ifthe compression head is to be increased, this can be done by reducingthe thickness of the lower bearing block before restoring it toposition.

The piston and connecting rod construction above described markedlyincreases the efilciency of an internal combustion engine in which it isemployed. Exceptional economies in liquid fuel and in lubricating oilare obtained. The life of the engine is extended due to the evendistribu- During the life of the engine, better attention may be givento its working organization due to the ease of access to the piston forreplacement of rings and adjustment of ings.

.What is claimed is:

l. The combination of a piston and a connecting rod, the pistoncomprising a ring-carrying head, a. central substantially continuoustubular part depending therefrom and open at the top, a removable capfor the top 'of said tubularpart, a skirt portion below and spaced awayfrom the said ring-carrying head, and a plurality of down wardly andoutwardly extending spaced legs united at their upper ends with saidtubular part and at their lower ends with the lower half of said skirtportion, the connecting rod comprising a spherical head disposed withinthe bore of said tubular part, and the piston also including upper andlower bearing elements for said spherical head carried by said tubuiarpart, the upper bearing element being removable from the top side of thepiston.

2. In a reciprocating piston engine, the combination of a piston, aconnecting rod, and means connecting the rod and piston adapted topermit rotative movement of the piston, said piston having means on thehead abetting variable rot'he connecting rod upper beartation thereof inone direction under working conditions.

3. The combination of a piston, a connecting rod, and means connectingthe rod and piston I extending from the lower end of said tubular partand having union with the skirt at the lower portion of said skirt, theconnecting rod comprising a spherical head disposed within the bore ofsaid tubular part. i

5. The combination of a piston and a connecting rod, the pistoncomprising a ring-carrying head, a central substantially continuoustubular part depending from said head, a skirt below and spaced fromsaid head, and spaced means extending from the lower end of said tubularpart and having union with the lower portion of said skirt, theconnecting rod comprising a spherical head disposed within the bore ofsaid tubular part.

6. The combination of a piston and a connecting rod, the pistoncomprising a ring-carrying head, a central substantially continuoustubular part depending from said head, a skirt below and spaced fromsaid head, spaced means extending from the lower end of said'tubularpart and having union with the lower portion of said skirt, the

connecting rod comprising a spherical head diswhich inclines from theplane of the top of one of i said faces toward the base of the next.

8. The combination of a piston and a connecting rod, the pistoncomprising a ring-carrying head, a centrally substantially continuoustubular part depending from said head, a removable cap at the top ofsaid tubular part, a skirt below said head and spaced therefrom, spacedmeans extending from the lower end of said tubular part and having unionwith the lower portion of said skirt, an upper bearing member removablyarranged in said tubular part, and a lower bearing member in saidtubular part, the connecting rod comprising a spherical head arrangedbetween said bearing members.

9. The combination of a piston and a connecting rod, the pistoncomprising a ring-carrying head, a central substantially continuoustubular part depending from said head, a skirt below and spaced fromsaid head, and spaced means extending downwardly from said tubular partand having union with the lower portion of said skirt, the connectingrod comprising a spherical head disposed within the bore of said tubularpart, a lower annular bearing within said tubular part surrounding theupper end of the connecting rod and bearing against the under side ofsaid spherical head and an upper hearing within said tu-' bular partbearing against the upper part of said spherical head.

10. The combination of a piston and a connecting rod, the connecting rodhaving a spherical head at its upper end, the piston comprising a headportion having a top part and a ring-carrying part and a centraldownwardly extending tubular bearing-carrying part provided withbearings for the spherical head of the connecting rod, and a skirtportion spaced from the ring-carrying part and from the bearing-carryingpart of the head portion, and three or more symmetrically arrangedstruts connecting-the skirt portion to one of said parts of the headportion.

therein, and a headed locking screw extending through the upper part 01said passage and screwed into the threaded bore in the end 01' theconnectingrod to seat its head against the ball, one of the threads ofthe end of the connecting rod being right-hand and the other left-hand.

JOHN SHEARMAN DONALDSON.

